Disorders of the retinal microvasculature are important in many diseases which impair vision. Retinal blood flow has been studied extensively, however retinal vascular pressures, which determine both capillary perfusion and filtration pressures, have not been directly measured. The experiments described in this proposal make use of newly developed micropuncture techniques to investigate the control of microvascular blood pressure and flow in the retina. The servonull micropuncture technique, in which micropipettes are used to measure hydrostatic pressure, will be used to measure vascular pressures in the intact retina of an anesthetized cat. The proposal is divided into several parts with considerable overlap in experimental technique and scientific purpose. In part one, pressures in retinal vessels will be determined under several physiological conditions which are related to autoregulatory mechanisms. Conditions to be tested include the effects of altered blood gas tensions and hyperglycemia. In part two, we note that our preliminary studies of retinal vein pressure contradict current understanding of retinal hemodynamics and we present two possible explanations for our data and propose experiments to test our hypotheses. In part three, the effect of a new fluorocarbon-based substitute, which may prove to be useful as a treatment for retinal vascular occlusion, will be tested for its effect on microvascular pressures and flow. In part four, we will use our recently developed model of retinal vascular occlusion to assess the effects of a retinal thrombosis on retinal microvascular pressures. These studies are expected to shed light on the etiology of several diseases which have circulatory components including diabetes, glaucoma, retinal edema and retinal occlusive disease. The cat will be the animal of choice for all these studies because of the comparative similarity of its retina and retinal vasculature to those of humans.